This invention relates to electronic devices, and more particularly to a packaged power semiconductor device with a metal back plate that is electrically isolated from the terminals of the device.
Electronic semiconductor device technology continues to rapidly advance, producing devices that achieve heretofore unattainable operating speeds, packing density, and high-temperature compatibility. This last characteristic, high-temperature compatibility, is one of more important features. High-temperature environments as well as high-power and high frequency applications are becoming increasingly important. The ability of electronics to withstand high-temperature environments such as gas-turbines, automotive engine compartments, materials handling and fabrication equipment, and aircraft subsystems makes possible many historically impractical electronic applications for these environments.
Many such high-power, high-temperature electronics applications inherently limit the ability to dissipate heat and power generated by the electronics. Thermal and power management as well as environmental protection of the electronics are therefore handled entirely by the electronics packaging. As a result, typical high-performance packaging criteria include mechanical strength, high thermal conductivity, close matching of device and package thermal expansion coefficients, low dielectric constant for accommodation of high frequency devices, and environmental protection, such as hermetic sealing.
In designing such packages, thermal management is importantxe2x80x94especially at high power generation levels which increase the amount of heat created. Heat decreases the performance and operating life of the transistor. Moreover, heat generated at the collector-base junction can create a temperature buildup which may eventually cause the device to short-circuit.
The power device may be mounted on a thermally conductive pad which acts as a heatsink and dissipates the heat generated by the power device. In order to prevent electrical losses, however, the thermally conductive pad must also be electrically insulating. Hence, a thermally conducting, electrically insulating material, e.g., ceramic, is used for the mounting pad.
In one embodiment, a packaged power device includes a substrate including a first conductive layer, a second dielectric layer, and a third conductive layer. The first conductive layer is bonded to the second dielectric layer, and the second dielectric layer is bonded to the third conductive layer. The first and third conductive layers are electrically isolated from each other. The substrate has a lower surface. A semiconductor die is bonded to the first conductive layer of the substrate. A plastic package encloses the die and has a lower surface. A curved backside includes the lower surfaces of the plastic package and substrate.
The curved backside of the device is attached to a heatsink to dissipate power generated by the power device and is configured to expand toward the heatsink during the operation of the power device, so that heatsink is in contact substantially with the entire backside of the power device. The backside of the power device includes a center portion directly underlying the die, a first outer portion extending outward from the center portion in a first direction and a second outer portion extending outward from the center portion in a second direction, wherein the center portion of the backside is substantially flat. The center portion of the curved backside of the device overlies flatly against a heatsink to dissipate power generated by the power device, and the first and second outer portions of the backside are provided above the heatsink without contacting the heatsink.
The power device is clipped or screwed to the heat sink. The power device is solder bonded to the heat sink. The center portion of the backside is solder bonded to the heatsink and the first and second outer portions are not solder bonded to the heatsink. The substrate is a direct bonded metal substrate. The substrate is a direct copper bonded substrate, wherein the first and third conductive layers are copper layers. The substrate is a direct aluminum bonded substrate, wherein the first and third conductive layers are aluminum layers.
The power device of claim 1, wherein the package has a length N1 and the backside has a pitch N2, wherein the pitch N2 is no more than 0.002xc3x97N1. The pitch is a vertical distance from a center of the backside to an edge of the backside. The power device of claim 1, wherein the backside has a pitch that is no more than 0.001 inch.
In another embodiment, a method of manufacturing a packaged power device includes providing a substrate having a curved surface; bonding a semiconductor die on the curved substrate; and forming a plastic package to enclose the die.